I got a SP4 (Surface Pro 4) for Christmas and all was working perfect, but then I turned it on one day, swiped up and then went to put in my pin but when I typed using the keyboard, nothing appeared. Then I tried typing in my pin with the screen and nothing appeared! So in other words I can't type in my pin I have created. I have tried disconnecting the keyboard, holding down the on Button to refresh and it's not working. So now I can't even go into my laptop! Please help me.
If that works, connect the external keyboard and see if you can type in the cortana search. If it doesn't work, you may want to try to restore your OS and if even that fails take it back for a replacement.